Polyalkylenecarbonate compositions stabilized against thermal degradation by thermolytic reactions with terminal hydroxyl positions, by end-capping or reaction of terminal hydroxyl, are disclosed and claimed in U.S. Pat. Nos. 4,066,630, 4,104,264 and 4,145,525, of common assignment herewith. The '264 patent, in particular, discloses such end-capped polyalkylenecarbonates stabilized by reacting the free terminal hydroxyl groups thereon with a hydroxyl reactive sulphur compound, among which are included, disulfides, such as dimethyl and diphenyl disulfide. In general the other sulphur compounds therein recited are sulfonyls and sulfinyls. According to the '264 patent, these sulphur compounds are reacted in an amount at least 20% in excess of the stoichiometric amount required to react with the terminal hydroxyl groups of the polyalkylenecarbonate (Column 3, lines 54-56). Residual reactant is, however, considered undesirable in any polymeric composition. Therefore, in the '264 patent process this reactant is removed, such as by extraction in a methanol precipitate (Column 4, lines 44-46).
The end-cap stabilized compositions of the aforementioned patents, as well as the stabilized composition and method of the present invention, are based upon polyalkylenecarbonates generally of the type prepared according to U.S. Pat. Nos. 3,585,168, 3,900,424 or 3,953,383. Such compositions are to be distinguished from polyarylenecarbonates, as to which thermal stabilization with antioxidant additives, especially including organophosphorous compounds, is well known.
Other resin antioxidant stabilizers are shown, in U.S. Pat. No. 4,032,510--Floyd et al, in which it is disclosed that resins, such as polyolefins, and most particularly these polymerized from alpha-olefins using a Ziegler-type polymerization catalyst, may be stabilized not only by phenolic additives but by reacted phenolics, particularly including end-reacted bisphenol sulfides. Extention of this teaching to polyalkylenecarbonates is not suggested, however.